Approved pharmacotherapies for alcohol dependence and PTSD show at best modest efficacy. Recent advances in the neurobiology of substance dependence and relapse suggest an important role of adrenergic systems. We have recently determined that the central nervous system active alpha-1 adrenergic receptor antagonist, prazosin, suppresses ethanol consumption in rats. We have also completed a preliminary clinical trial which suggests that prazosin is well tolerated, and when compared to placebo, it significantly reduces alcohol consumption among alcohol dependent men. We propose to replicate and extend these findings by conducting an 8-week, randomized, two group parallel-design, double-blind, placebo-controlled trial to evaluate the efficacy of prazosin for decreasing alcohol use and PTSD symptoms in individuals (N=60) seeking treatment for alcohol dependence (AD) who have comorbid PTSD. After randomization a 2-week titration period will be followed by 6 weeks of stable dose on prazosin or placebo. Study participants will also receive Medical Management, a behavioral intervention with demonstrated efficacy as a platform for pharmacologic treatment of AD. We will monitor substance use, subjective impressions of alcohol's reinforcing properties, substance craving, PTSD symptoms, and medication compliance via toll-free telephone calls to an interactive voice response (IVR) system. Outcome measures include IVR reports of use and PTSD symptoms, the Timeline Follow-back, the PTSD Symptom Scale, Interview form, Penn Alcohol Craving Scale, the Addiction Severity Index, urine toxicology analysis, and breathalyzer readings. Medication compliance will be monitored with riboflavin trace and pill counts and supported by the IVR technology. Data will be analyzed using hierarchical linear models.